Antenna Gain Pattern
Understanding Antenna Gain Patterns
The antenna gain pattern is the most complete characterization of an antenna's radiation behavior. It tells the engineer exactly how much signal is radiated (or received) in every direction relative to an isotropic antenna.
Gain Pattern Features
- Main beam: The direction of maximum gain. Defined by the beam center and beamwidth.
- Sidelobes: Secondary maxima around the main beam. Specified by sidelobe level relative to main beam peak.
- Nulls: Directions of zero (minimum) radiation between lobes.
- Back lobe: Radiation in the opposite direction to the main beam. Front-to-back ratio specifies this.
Pattern Cuts
- E-plane: Cut containing the electric field vector and beam maximum. Often shows the narrower beamwidth.
- H-plane: Cut containing the magnetic field vector and beam maximum. Often shows the wider beamwidth for rectangular apertures.
Frequently Asked Questions
What is an antenna gain pattern?
The gain pattern shows antenna gain as a function of direction in space. It reveals the main beam, sidelobes, nulls, and back radiation. Peak gain occurs at the main beam direction. Presented as 2D cuts or 3D surfaces.
How is the gain pattern measured?
In an anechoic chamber or outdoor range, the antenna rotates while a fixed source transmits. Received power vs angle gives the pattern. Near-field scanning measures amplitude and phase on a close surface, then transforms to the far-field pattern mathematically.
What is front-to-back ratio?
Front-to-back (F/B) ratio is the gain in the main beam direction minus the gain in the directly opposite direction. 20 dB F/B means the antenna radiates 100x more power forward than backward. Higher F/B is better for directional communications and reducing interference.